The invention relates to a light metal cylinder crankcase for combustion engines wherein the light metal cylinder crankcase includes cylinder bushings. It also relates to a procedure for manufacturing cylinder bushings for a cylinder crankcase and to a procedure for manufacturing a cylinder crankcase with such cylinder bushings.
For purposes of lightweight construction, grey cast iron is currently being substituted by aluminum alloys in cylinder crankcases of combustion engines for motor vehicles. While grey cast iron is also suitable for the cylinder bearing surface, aluminum cast alloys are reinforced in this area by cylinder bushings.
Known from DE 196 05 946 C1 is a cylinder bushing made out of a molybdenum running layer and an outside aluminum alloy layer, whose outside is profiled. Both layers are formed via thermal spraying on a rotating mandrel. Using molybdenum, an anti-adhesive, a mandrel with a hard chromium layer, etc. reduces the adhesion of the running layer to the mandrel to a point where the bushings can be taken off the mandrel.
When casting the cylinder crankcase, the cylinder bushings arranged on barrels in the mold with their profiled outside surface are positively joined with the casting material. The heavy molybdenum running layer gives the known cylinder bushing considerable weight. In addition, there is a danger that the bushings will loosen, the cylinder will shift, and hence the blow-by values will increase. Residues from the combustion process can also get into the micro-gap at the phase boundary between the casting material and the bushings.
To improve the bonding of the cylinder bushing to the casting material of the cylinder crankcase, DE 196 34 504 A1 describes abrasive blasting of the surface of the cylinder bushing with sharp-edged particles to achieve a roughness of 30–60 μm in the form of pyramidal protuberances.
Since the oxide skin on an aluminium body to be poured into an aluminium casting material prevents bonding to the casting material, DE 197 45 725 A1 describes mechanically destroying the oxide skin on the pouring body through thermal spraying, wherein the resultant oxide particles are distributed in the spraying layer. In addition, the spraying material particles that did not completely melt on impact project out of the spraying layer, which improves the connection with the casting material. A nickel or molybdenum alloy is used as the spraying material.